1. Field of the Invention
This invention relates to a multi-band planar antenna for wireless communication devices and relates specifically to a multi-band planar antenna which is compact and which does not require additional cabling or connections to the transmitter/receiver.
2. Description of the Related Art
For a given physical size and set of antenna performance parameters, such as gain and antenna pattern, multi-band antennas have often been of lower performance than single band antennas of the same size, or conversely have been physically larger than single band antennas of the same performance. Additionally, multi-band antennas have often been more complex in structure than single-band antennas, hence multi-band antennas have been of higher cost than single band antennas. In many cases where multi-band antennas have been applied the multi-band antenna impedance characteristic is not matched to 50 ohms at all the desired bands, hence requiring a matching network to be used in conjunction with the multi-band antenna. In many applications, a multi-band antenna is desired of the same size, cost, and simplicity of a single-band antenna. The need for planar antennas has been well-described in U.S. Pat. Nos. 6,157,344, 6,249,254 and 6,037,525. Thus, there is a need for planar, multi-band antennas which have the advantages of a planar antenna such as in the ""344 patent but that operates at two or more frequencies and are no larger than the antenna of the ""344 patent. In particular, the telematics market desires a dual-band antenna for the two primary network frequencies (e.g., 860 MHz [AMPS] and 1920 MHz [PCS]).
U.S. Pat. No. 6,307,525 pertains to a multi-band antenna which combines elements of a design of U.S. Pat. Nos. 6,157,344 and 6,249,254 with a multiplexer capable of separating the RF energy based on frequency. While the antenna of the ""525 patent performs exceedingly well and has been successfully commercialized, it is relatively large and in general is larger than the area of the antennas which it replaces.
Further, the introduction of the multiplexer circuit introduces some losses which reduce the gain of the antenna in the ""525 patent, and in some cases, the patterns of the antenna radiation are affected by the presence of the multiplexer. The main advantage of the antenna in the ""525 patent is the single port and the planar shape thereof.
A compact, multi-band planar antenna is provided which consists of a substrate having opposite sides with the substrate comprising a commercial PCB laminate. A ground plane is formed on one side of the substrate by known PCB processing techniques. On the other side of the substrate, an antenna element or radiating element is formed by the same processing technique. The shape of the antenna element is generally triangular in shape with a feed point being provided at the apex thereof. An opening or cut-out portion is formed in the antenna element which provides for a multiplicity of current paths giving rise to the multi-banding characteristics of the invention. In some embodiments, a second ground plane is formed on the substrate on the same side as the antenna element. In some embodiments, a matching network is formed on the substrate which is connected to the feed point of the antenna element in order to increase the bandwidth of the antenna or to improve the impedance matching. In some embodiments wherein a matching network is utilized, the matching network is comprised of a network of microstrip transmission lines with the ground plane being utilized as the ground plane side of the transmission lines. In some embodiments, the opening formed in the antenna element is modified by partially filling it with a second antenna element.
In the present invention, the advantages of the antenna of the ""525 patent are maintained, but the size is similar to the antenna as described in the ""344 and ""254 patents operating at the lowest of the multi-band frequencies. Therefore, in the present invention, the advantages of the antenna of the ""344 patent and the ""254 patent are fully retained without additional size, cost, or manufacturing difficulty, with additional frequencies of operation being created with similar pattern and gain characteristics of the antenna of the ""344 and ""254 patents.
It is therefore a principal object of the invention to provide an improved multi-band antenna.
A further object of the invention is to provide a compact, multi-band planar antenna.
Yet another object of the invention is to provide a multi-band planar antenna which does not require additional cabling or connections to the transmitter/receiver of the wireless communication device.
Still another object of the invention is to provide a compact, multi-band planar antenna which has satisfactory gain performance.
Still another object of the invention is to provide a planar antenna which permits multi-banding in any application which can be served by a single band antenna according to the ""344 patent.
Still another object of the invention is to provide an antenna of the type described which may be modified in order to alter the operating frequency, improve the bandwidth, or otherwise modify the performance characteristics of the antenna.
These and other objects will be apparent to those skilled in the art.